For example, pump assemblies which comprise a wet-running electric motor, in which a can separating the rotor space from the dry stator space is arranged, are applied as circulation pumps in heating installations. As a rule, these pump assemblies are designed such that there is a stator housing, in which the stator with the can is arranged, and a pump housing, in which an impeller rotates. The stator housing, and the pump housing, are connected to one another, for example screwed to one another. The impeller is arranged on a rotor shaft of a rotor which is rotatably mounted in the stator or in the can. If the pump housing and the stator housing are connected to one another, it is necessary to center the stator with the impeller in the inside of the pump housing, so that the impeller is arranged in the pump space of the pump housing in a defined manner.